Imaging devices such as cameras are embedded into a wide variety of products today. When a camera is mounted on a small-sized electronic apparatus such as a cellular phone or a notebook computer, downsizing of the camera itself is strongly demanded.
An autofocus lens is incorporated into a camera in some cases. In such a case, downsizing of an actuator that displaces the lens is strongly demanded. As a small-sized actuator, an actuator that displaces a movable object by driving an piezoelectric element is known (cf. Patent document 1). In the actuator, vibration produced upon application of a voltage waveform to a piezoelectric element is transmitted, through a shaft coupled to the piezoelectric element, to a lens barrel slidably engaged with the shaft. By setting an appropriate waveform of the voltage waveform applied to the piezoelectric element, the speed of expansion and the speed of contraction of the piezoelectric element are differentiated. By the friction between the lens barrel and the shaft and the inertia of the lens barrel, the lens barrel undergoes or does not undergo displacement depending on the expansion and contraction state of the piezoelectric element.
For example, when the piezoelectric element expands in a short time, the lens barrel is not substantially displaced. When the piezoelectric element expands in a relatively long time, the lens barrel is displaced. On the contrary, when the piezoelectric element contracts in a short time, the lens barrel is not substantially displaced. When the piezoelectric element contracts in a relatively long time, the lens barrel is displaced.
By continuously applying a given voltage waveform (e.g. a sawtooth-shaped voltage waveform) to the piezoelectric element, the lens barrel can be moved in a desired direction on the shaft with which the lens barrel is engaged.
Patent document 1 discloses a structure in which a piezoelectric element and a drive shaft coupled to the piezoelectric element are supported by a special frame. Patent document 2 discloses a structure in which a drive device is produced with inclusion of a spindle. Patent document 3 discloses a drive device of the similar structure. Patent document 4 discloses a drive device in which a piezo element is urged by a leaf spring so that the piezo element and a shaft member are engaged with each other (cf. FIG. 10 in Patent document 4).